construction and characterisation of a particle magnifier helene holmgren

Construction and Characterisation of a Particle Magnifier

Helene Holmgren

Outline

• Background

• Condensation Particle Counter – CPC

• Pulse Height Analysis - PHA

• Particle Magnifier

• Future Applications

• Take Home Messages

Background

• Particle formation and growth

• Clusters - particle

• Nanoparticles–Too small to scatter enough light to be detected by

optical methods

–Too small to carry significant charge to be classified according to electrical mobility

–Diffusion losses

Condensation Particle Counter

• 2.5 – 1000 nm (TSI)

• <10,000,000 particles cm-3 (TSI)

• Measures particle number concentrations, but all information regarding size is lost

Condensation Particle Counter

• Heated saturator–Vaporisation of

working medium

• Cooled condenser–Supersaturation

–Condensation and growth

• Optical detector–Light scattering

Condensation Particle Counter

• S saturation ratio

• P actual vapour partial-pressure (Pa)

• P saturation vapour pressure (Pa)

• g surface tension (N m-1)

• M molecular weight (kg mol-1)

• r density (kg m-3)

• R universal gas constant (J K-1 mol-1)

• T absolute temp (K)

• d Kelvin diameter (m)

rRTd

gM

P

PS

s

4exp

Pulse Height Analysis

• Measures pulse heights produced when particles pass laser beam

• Particles <15 nm (Saros et. al 1996)

–Pulse height increases with particle size

• Particles > 15 nm (Saros et. al 1996)

–All particles grow to the same size

Particle Magnifier

• Detect, count AND size nanoparticles

• Push size detection limit downwards–Optimise saturation and cooling systems

–Find the most favourable working medium

• Minimise diffusion losses– Instrument design

condenser

particles

saturator

optical detection

Particle Magnifier

Particle Magnifier

• Grimm Dust Monitor

• IR-laser

• Light-scattering

• Pulse Height Analysis

Particle MagnifierGrim m

0200400600800

100012001400160018002000

particle diam eter (µm )

par

ticl

es/li

tre

ΔT = 20 K

0

20000

40000

60000

80000

100000

120000

140000

160000

particle diam eter (µm )

par

ticl

es/li

tre

ΔT = 22 K

0

20000

40000

60000

80000

100000

120000

140000

160000

particle diam eter (µm )

par

ticl

es/li

tre

ΔT = 24 K

0

20000

40000

60000

80000

100000

120000

140000

160000

particle diam eter (µm )

par

ticl

es/li

tre

Future Applications

• Field measurements–SOA formation

–Terpenes emitted from vegetation

• Laboratory studies–SOA formation

–Connect to laminar flow tube (Emanuelsson)

Take Home Messages

• It is possible to obtain number-size distributions of nanoparticles by combining the principles of CPCs with PHA technique

• Particles <10 nm are activated at different sites in the condenser, and grow to different sizes

• Particles >10 nm are activated near the entrance of the condenser, and grow to the same size

References

• Saros, M., et al., Ultrafine aerosol measurement using a condensation nucleus counter with pulse height analysis. Aerosol Science and Technology, 1996. 25(2): p. 200-213.